1. Field of the Invention
The present invention relates to a winding bobbin around which a conductor is wound in several layers and a rotating electric machine using the winding bobbin.
2. Description of the Related Art
As a conventional winding bobbin, the following winding bobbin is known. The winding bobbin includes: a winding portion around which a conductor is wound; and a first flange portion and a second flange portion respectively provided on both sides of the winding portion. A groove having a depth equal to an outer diameter size of the conductor is formed in the winding portion between the first flange portion and the second flange portion (for example, see JP 08-316058 A (FIG. 1)).
In the case of the above-mentioned conventional winding bobbin, the conductor is wound around the winding portion from the first flange portion toward the second flange portion. When the conductor is wound to reach the second flange portion, the conductor is then wound back from the second flange portion toward the first flange portion. When the number of layers formed by winding the conductor is even, a winding-start side lead wire of the conductor and a winding-end side lead wire of the conductor are led out in the same direction.
If it is desired to lead out the winding-start side lead wire and the winding-end side lead wire in the same direction even in the case where the number of layers formed by winding the conductor is odd, the groove is formed in the winding portion to prevent the effort of winding back the conductor in another extra layer to fabricate a rotor coil with an increased outer diameter size or to prevent the number of layers formed by winding the conductor from being reduced by one to fabricate a rotor coil with a reduced outer diameter size.
More specifically, in this case, a winding start portion of the conductor is caused to pass along the groove to the second flange portion, thereby allowing the winding of the conductor to be started at the second flange portion. As a result, even when the number of layers formed by winding the conductor is odd, the winding-start side lead wire and the winding-end side lead wire can be led out in the same direction while a desired outer diameter size of the rotor coil is ensured.
For the conventional winding bobbin, however, it is necessary to additionally form the groove having the depth equal to the outer diameter size of the conductor between the first flange portion and the second flange portion. Therefore, there is a problem that the fabrication of the winding bobbin becomes complicated.